The present invention pertains to a device for shifting a mechanical shifting device between a first shifting state and at least one second shifting state, especially for engaging and disengaging a parking brake for an automatic transmission.
Automatic transmissions with a mechanical parking brake have been known from the state of the art. At least four modes of operation, which correspond to the following shift positions of a gearshift lever, namely, xe2x80x9cP,xe2x80x9d xe2x80x9cR,xe2x80x9d xe2x80x9cNxe2x80x9d and xe2x80x9cD,xe2x80x9d are usually associated with a conventional automatic transmission for motor vehicles. In the individual shift positions, xe2x80x9cPxe2x80x9d designates the state xe2x80x9cParking,xe2x80x9d in which the transmission is usually blocked mechanically against the transmission of movements by the parking brake. xe2x80x9cRxe2x80x9d designates the xe2x80x9creverse movement,xe2x80x9d xe2x80x9cDxe2x80x9d designates the xe2x80x9cforward movement,xe2x80x9d and the shift position xe2x80x9cNxe2x80x9d corresponds to the xe2x80x9cneutral operation,xe2x80x9d in which there is no mechanical coupling between the engine and the wheels.
A usual safety requirement is that the mechanical parking brake of the automatic transmission can always be engaged or is always engaged with the vehicle not moving.
This safety requirement can be satisfied relatively easily with an automatic shifting, in which a mechanical transmission member, e.g., a gearshift cable or a gearshift linkage, is provided between the gearshift lever and the automatic transmission, because a coupling is forced to take place between the actual shifting state of the transmission and the indicated shifting state of the gearshift lever because of the mechanical transmission member, at any rate as long as the mechanical transmission member is not defective. The gearshift lever can be brought into the shift position xe2x80x9cPxe2x80x9d and the automatic transmission can be shifted via the mechanical coupling into the corresponding state with the parking brake engaged even in case of a power failure in the vehicle.
However, electromechanical transmission members have recently been developed for the automatic shifting, wherein a mechanical coupling between the automatic transmission and the gearshift lever is no longer present. The shifting states of the gearshift lever are detected electronically in this case and are sent in the form of electric signals associated with the shifting states to a device (transmission actuator mechanism), which brings the automatic transmission into the mode of operation corresponding to the shift position of the gearshift lever instead of the mechanical transmission member. Such an electromechanical shifting operation is also called xe2x80x9cshift by wirexe2x80x9d in English.
However, it is possible with the electromechanical coupling between the gearshift lever and the automatic transmission that in the case of a power failure in the vehicle, a different mode of operation is set for the transmission than is indicated by the gearshift lever, because the gearshift lever can be actuated independently from the transmission actuator mechanism. However, the above-mentioned safety requirement can thus no longer be satisfied in all cases.
The basic object of the present invention is to provide a device with which the above-mentioned safety requirement for an automatic transmission can be satisfied even in case of the use of an electromechanical transmission member.
The device according to the present invention for shifting the gears of a mechanical shifting device between a first shifting state and at least one second shifting state has an adjusting member coupled with the shifting device shifting between the shifting states, wherein the adjusting member can be coupled with a control member via a coupling device.
A certain position of the adjusting member is associated with each shifting state of the shifting device, so that the shifting device can be shifted into any desired shifting state from the first shifting state and from the at least one second shifting state by the adjusting member being brought into the position associated with the desired shifting state. A change in the position of the adjusting member may be brought about, e.g., by displacement, rotation or pivoting.
In the coupled state, the adjusting member can be driven or actuated by the control member, and the control member itself is actuated or driven by a drive device. The adjusting member can consequently be brought into the different positions associated with the shifting states by driving the control member. A certain position of the control member, into which this control member can be brought by means of the drive means, is in turn associated for this with each of the aforementioned positions of the adjusting member.
The coupling device can be actuated by means of an electric signal, i.e., the adjusting member is coupled with the control member by this coupling device when the electric signal assumes a certain state. It may be nearly any state as long as it is ensured that it differs from the signal state occurring in case of loss of the electric signal, e.g., a power failure. In case of loss of the electric signal, the coupling between the adjusting member and the control member is then released by the coupling device, so that these two members are again uncoupled from one another.
For the reliable resetting of the shifting device into the first shifting state in case of loss of the electric signal, a spring means is coupled with the adjusting member and with an abutment, the spring means being tensioned in each shifting state that is different from the first shifting state in relation to the adjusting member such that in case of an uncoupling between the adjusting member and the control member, the adjusting member is shifted by the spring means into the position associated with the first shifting state while the tension of the spring means decreases, as a result of which the shifting device is also shifted into the first shifting state. Since the spring means is coupled with the adjusting member and the abutment, the tension of the spring means that is necessary for the resetting of the adjusting member into the position associated with the first shifting state can be built up by a change in the relative position between the adjusting member and the abutment or by a relative movement of the adjusting member and the abutment.
The device according to the present invention may be used wherever a certain shifting state of at least two shifting states of a mechanical shifting device shall be engaged with certainty in case of a power failure. However, the device according to the present invention is preferably used to engage and disengage a parking brake of an automatic transmission. The shifting device is now designed as the parking brake of the automatic transmission, where the first shifting state corresponds to the state of the engaged parking brake and the at least one second shifting state corresponds to the state of the disengaged parking brake.
The adjusting member may be coupled with the shifting device with a common lever mechanism. However, the adjusting member is preferably coupled with the shifting device via a shaft, in which case the shifting device is shifted by a rotary movement of the shaft between the first and at least one second shifting states. The adjusting member is connected to the shaft, rotating with it in unison in this case.
In the coupled state, the control member may transmit a translatory movement, which can be converted at the adjusting member into a rotating movement for shifting between the different states. However, the control member is preferably mounted rotatably in relation to the shaft, in which case the adjusting member and the control member are connected to one another rotating in unison in the coupled state. The shaft can thus be rotated by a rotary movement of the control member in the coupled state via the adjusting member for shifting the shifting device between the shifting states.
The coupled state of the adjusting member and the control member may be embodied by means of a common positive-locking and non-positive connection. For example, the coupled state may be embodied according to the principle of a friction clutch, in which case the adjusting member, the control member and the coupling device are designed according to the design of such a friction coupling. However, the adjusting member and the control member are preferably designed such that a toothed brake (jaw clutch) is formed by these two members.
To form a jaw clutch, both the adjusting member and the control member are designed as disks, whose surfaces located opposite each other are provided with a plurality of teeth each. The adjusting member and the control member are held against one another in the coupled state by a coupling force applied by the coupling device, with the teeth of the control member engaging the spaces between the teeth of the adjusting member and vice versa. The teeth of the adjusting member are now in functional connection with the teeth of the control member, as a result of which a connection rotating in unison is established between the control member and the adjusting member as long as the coupling force is maintained by the coupling device. Furthermore, the geometric design of the teeth is such that a releasing force, which pushes the control member and the adjusting member apart, acts on the two members during the transmission of a torque from the adjusting member to the control member or vice versa. If the coupled state between the adjusting member and the control member shall be maintained, the amount of the coupling force must therefore always be greater than or at least equal to the amount of the releasing force. When the coupling force is eliminated and a torque is transmitted at the same time from the adjusting member to the control member or vice versa, the control member and the adjusting member are moved apart relative to one another until the teeth cease to engage the tooth spaces. The jaw coupling thus has the advantage that the IBM connection rotating in unison between the adjusting member and the control member is automatically released when the two members are no longer held in contact with one another by the coupling force. The jaw coupling is preferably designed such that the control member is moved away from the adjusting member due to the releasing force.
The spring means may be formed by any mechanical spring that is suitable for resetting the shifting device located in the at least one second shifting state into the first shifting state in the uncoupled state. However, the spring means is preferably a coil spring, leg spring or helically wound spiral spring fastened to the adjusting member and the abutment, in which case the resetting of the shifting device into the first shifting state takes place by the connection rotating in unison between the adjusting member and the shaft.
To guarantee reliable resetting of the shifting device into the first shifting state, the spring means must have a certain resetting tension in the second shifting state. It may be necessary for this to provide a certain minimum pretension for the spring means already in the first shifting state.
The spring means is coupled with the adjusting member and with the abutment, the abutment being provided according to a first alternative at the automatic transmission or at a site that is stationary relative to the automatic transmission. If the adjusting member is brought into the position associated with the second shifting state, e.g., by a rotary movement to shift into the second shifting state, the spring means is tensioned up to the resetting tension at the same time.
However, the consequence of the arrangement of the abutment according to the first alternative is that the work needed to tension the spring means must be performed each time when shifting from the first shifting state into the second shifting state takes place. Furthermore, the work to be performed for shifting becomes greater and greater the farther the adjusting member must be moved or rotated for this. This effect may be undesired in some types of application of the device according to the present invention.
The abutment is therefore provided at the control member according to a second alternative. In this case, the control member is pretensioned in relation to the adjusting member in the uncoupled state up to the resetting tension. The adjusting member and the control member are coupled with one another via the coupling device only thereafter. It is therefore no longer necessary to perform work for tensioning the spring means in the coupled state during the shifting from the first shifting state into the at least one second shifting state, because there is no relative movement between the adjusting member and the control member or the abutment. The tension of the spring means is set constantly at the resetting tension in the coupled state, so that the tension of the spring means according to the second alternative is constant in each shifting state. In order for the adjusting member to be able to reset by the spring means into the position associated with the first shifting state in the uncoupled state, the control member must be fixed during the resetting operation in relation to the adjusting member, so that the spring means can relax or reduce its tension only by the resetting of the adjusting member. This fixation of the control member may take place, e.g., by the control member being driven by the drive means via a transmission with self-locking, such as a worm gear.
The coupling device has the task of coupling the control member and the adjusting member with one another. To perform this task, the control device may be moved, e.g., by the coupling device toward the adjusting member to establish a mechanical contact, and the coupling device applies a coupling force by which the adjusting member and the control member are brought into contact with one another and are held in contact with one another. Furthermore, the coupling between the adjusting member and the control member shall again be released by the coupling device under certain conditions. This can be achieved, e.g., by the coupling device not applying any coupling force on the control member or on the adjusting member any longer in the uncoupled state. The coupling device may be designed such that the control member is moved away from the adjusting member or vice versa by the coupling device to assume the uncoupled state.
The coupling device may have, e.g., a pneumatic, hydraulic or electrostatic design. However, the coupling device preferably has a magnetic design, in which case the coupling device has a magnetizable area each at both the adjusting member and the control member, and at least one of the magnetizable areas is formed by an electromagnet that can be activated by the electric signal.
According to a simple embodiment of this preferred magnetic coupling device, the electromagnet is arranged at the adjusting member and the magnetizable area made of ferromagnetic material is arranged at the control member. When an electric current forming the electric signal is flowing through the electromagnet, the magnetic field generated by the electromagnet cooperates with the ferromagnetic area at the control member such that the control member is pulled by the electromagnet. The pulling force generated by the activated electromagnet in cooperation with the ferromagnetic area, acting as a coupling force, causes the control member and the adjusting member to be brought into contact with one another and to be firmly held together. If the electric current fails for any reason, the magnetic field of the electromagnet also collapses, and no coupling force is generated any longer to hold together the adjusting member and the control member.
It is, of course, also possible to arrange the electromagnet at the control member and the ferromagnetic area at the adjusting member. Furthermore, the ferromagnetic area may also be replaced by a second magnet, especially a second electromagnet.
If the device according to the present invention is integrated within a larger system comprising a plurality of components with a system control, the failure of individual components of the system is possible without the electric signal failing. Nevertheless, it may be important for safety reasons for the shifting device to be shifted in such situations into the first shifting state. The signal state can for this reason also be brought about by the system control in a controlled manner by the electric signal being brought by the system control into the state that it assumes in the case of its failure.